The Church of God teaches matters of the law that are not taught in Protestantism, as well as many prophecies related to Daniel and Revelation. However, their doctrine is modeled after that of the Sabbatarian Church. The doctrines of the Sabbatarian Church are based on books written by a woman named Ellen G. White, whose writings are 99% consistent or similar to those taught by the Church of God. The similarity between the doctrines of the Church of God and those of Ellen G. White is due to the fact that the founder of the Church of God, Ahn Sang-hong, was immersed in the doctrines of Ellen G. White and imitated them.

The Church of God claims that the Sabbath and Passover are the marks of God and that Sunday worship and Christmas are the marks of Satan, which is also a quote from Ellen G. White's doctrine. The differences and similarities between the doctrines of Ellen G. White and the Church of God include the following

1.Differences

1)The Church of the Sabbath observes the Sabbath based on sunset from Friday evening to Saturday evening, while the Church of God observes the Sabbath based on sunrise from Saturday morning to Sunday morning.

2) Sabbatarianism claims that the Sabbath is the seal of God, while the Church of God claims that the Passover is the seal of God.

3) Sabbatarianism claims that the Holy Spirit came upon the world in 1844, the year Sabbatarianism was founded, and the construction of the temple began, but Ahn claims that the world ended with the completion of the temple in 2012, 168 years from 1844.

4) Sabbatarianism claims that Jesus came to Sabbatarians by the Holy Spirit, while the Church of God claims that Jesus is returning in the flesh.

2.Similarities

1)The 2300 days and nights prophecy taught by Ahnsahnghong Ahn is a quote from the doctrine of Ellen G. White.

2)The prophecies in Daniel 2, 7, 8, and Revelation 12, 13, and 17 are quotes from Ellen G. White. It was Ellen G. White who interpreted the beast coming up out of the earth in Revelation 13 as the United States.

3)The actions of Moses and Jesus in moving in accordance with the feasts also mimicked the doctrines of Ellen G. White.

4)The temple system and the Day of Atonement ordinances also cited Ellen G. White's doctrine.

5)The Last Supper and Passover also cited Ellen G. White's doctrine.

6)The woman's remaining descendants also cited Ellen G. White's doctrine.

7)The millennial kingdom and the city of God, Jerusalem, are also quotes from the doctrine of Ellen G. White.

8)The brass serpent and cross incident also cites Ellen G. White doctrine

9)The seven feasts and prophecies are quotes from the doctrines of Ellen G. White.

In conclusion, there are very few doctrines that Ahn found through his own research, and most of them are quoted from the doctrines of Ellen G. White. For reference, the link below shows a list of the books written by Ellen G. White, which shows that the doctrines of the Church of God are based on the doctrines of the Sabbatarian Church.

https://www.syu.ac.kr/egw/original-text/read-original/book-list/ 

It should be noted that the Sabbatarian Church has long regarded Ellen G. White's prophecy as a false prophecy, but recently there has been some consensus that her prophecy should be studied again, and they have begun to do so. Because Ahn founded the Church of God based on Ellen G. White's false prophecies, the eschatology preached by the Church of God never came to pass.